"Prime Minister Netanyahu came to Moscow," Medvedev told CNN. "He did this under a closed regime, this was his decision. I don't understand what this was connected with, but sometimes our partners decide it this way," he added, offering no details.

Broader cooperation?Some experts say the two sides have been edging toward a wider strategic compact for some time.

"One of the key goals of the Netanyahu government is to establish a strategic partnership with Russia," says Yevgeny Satanovsky, president of the independent Institute for Middle East Studies in Moscow. "It's possible that such a relationship could become as important for Israel as its bond with the US."

Cooperation between Russia and Israel has grown in recent years, including recent Russian arms purchases from Israel, and many former Soviet Jewish emigrés have returned to Russia to take advantage of exploding job opportunities and the apparent easing of anti-Semitism in the country.

Russian missile sale would 'signal war'No one knows for sure what was discussed in the high-level meetings between Israeli and Russian leaders, but experts say the only subject that would warrant such urgent top-level shuttle diplomacy is Russia's outstanding contract to provide ultramodern S-300 air-defense systems to Iran.

The latest version of the weapon, known as the "Favorit", can simultaneously engage 12 targets flying at any altitude from about 30 feet to 20 miles, and strike them at a range of up to 75 miles away.

Russia and Iran signed a contract for the weapons two years ago, but Russia has yet to deliver.

"The S-300 would give such good protection to the Iranian nuclear project that if these Russian missiles come to Iran, that will probably be the signal for war," says Mr. Satanovsky.

"Such missiles will be seen as being for one purpose only, to defend an Iranian nuclear bomb," he says.

Russia's credibility on the lineBut Russia has a strong interest in following through with the Iranian deal, says Sergei Markov, a pro-Kremlin deputy of Russia's State Duma, the lower house of parliament.

"For our military-industrial complex, it's a matter of survival," Mr. Markov says. "This is not just a very lucrative contract, it also puts Russian credibility on the line. If we don't deliver on this deal, no anti-American regime will believe in us as a supplier and buy our weapons. Since pro-American regimes don't buy Russian weapons, that would be the end of Russia as an arms exporter."

A report this week in the Israeli daily Haaretz suggested that the main purpose of Netanyahu's secret visit to the Kremlin was an effort to persuade Russian leaders to hold off on providing the missiles to Iran, and it added that Israel has asked all its friends in the West to put pressure on Moscow to cancel the sale.

"Georgia was militarized with Israeli help, and this has been a cause of great dissatisfaction for us," says Markov.

Already, there is a precedent for Russia backing off on foreign arms sales in exchange for Israeli cooperation on Georgia.

One of the weapons Israel provided to Georgia, along with training for Georgian troops, was unmanned drones – an increasingly popular, hi-tech battlefield tool that Russia is far behind on developing.

This past spring, Moscow halted progress on the sale of advanced fighter planes to Syria in exchange for the opportunity to buy unmanned drones from Israel, according to the Jerusalem Post.

But while the precedent for Israeli-Russian cooperation is clear, it is unknown what another such deal would include.Medvedev revealed no change of heart on Iran sanctions

In his CNN interview, Medvedev offered few clues to suggest that Russia's position, which has been to resist tough sanctions against Iran, might be changing.

He scolded Iran, saying it must cooperate with the international community in its drive to acquire nuclear technology, but also suggested that Israel was overreacting to the threat of Russian S-300 missiles.

"Supplies of any weapons, especially defensive weapons, cannot increase tension; on the contrary, they should ease it," he said.

And he suggested Russia would oppose any Israeli military strike against Iran.

"This is the worst thing that can be imagined," Medvedev said. "What would happen after that? Humanitarian disaster, a vast number of refugees, Iran's wish to take revenge - and not only upon Israel, to be honest, but upon other countries as well.

"But my Israeli colleagues told me they were not planning to act in this way, and I trust them," Medvedev added.